1. Technical Field
The present invention relates to an optical member with a retardation control function and a liquid crystal display using the optical member, and in particular, to a liquid crystal display or an electroluminescence display excellent in the display quality and an optical member used therefor.
2. Background Art
In recent years, from high display characteristics, liquid crystal displays of In-Plane Switching mode and Multi-Domain Vertical Alignment mode are widely used. In order to expand a viewing field angle in the liquid crystal displays, a method where a film having the optical anisotropy is adhered to the outside of a liquid crystal cell has been widely used.
Recently, instead of the retardation film, a retardation layer that is formed in a cell with a liquid crystal material has been proposed. The retardation layer is called a so-called in-cell type. As a method of forming a retardation layer inside of a liquid crystal cell by use of a liquid crystal material such as a crosslinkable liquid crystal or a polymer liquid crystal, several methods have been proposed. For example, there has been proposed a method where an alignment film is formed in advance on a surface of a base material that forms the retardation layer by means of a rubbing method, an optical orientation method, an ion beam method or the like, followed by coating a liquid crystal composition containing a liquid crystal material on the alignment film in a base material thereof to form a retardation layer (for example, Patent document 1 below). Alternatively, corresponding to problems such as thinning of display devices and reduction of producing steps, a crosslinkable liquid crystal material composition for obtaining a retardation layer that realizes homeotropic alignment without using an alignment film is under study (for example, Patent document 2 below).
A substrate having the retardation layer is adhered to a counter substrate with a definite gap disposed therebetween and a driving liquid crystal material is filled into the gap portion to constitute a liquid crystal cell. At that time, in order to secure a definite gap between two substrates, a method where glass or transparent resin beads are sprayed is generally used (for example, Patent document 3). In the above method, the surface of the retardation layer and beads come into point contact. However, since the retardation layer is generally low in the hardness, there is a problem in that, when the retardation layer comes into point contact with the beads, the beads subside in the retardation layer, thereby making it difficult to secure a definite cell gap.
In view of the above problems, a technology of a method where columnar structures are disposed on a retardation layer to realize a highly precise cell gap is disclosed (for example, Patent document 4 below). In the columnar structure, a contact portion with a retardation layer becomes a surface. Accordingly, the columnar structure is inhibited from subsiding in a retardation layer, whereby a highly-controlled cell gap control is readily applied all over an entire effective display area.
Here, in many liquid crystal displays of a normally black mode, in general, a liquid crystal cell per se is designed so as to obtain the retardation of λ/2 that is a design wavelength at the time of white display when a voltage is applied. The retardation of the liquid crystal cell is expressed by Δn (birefringence anisotropy)×d (thickness). That is, in order to enable to display uniformly over an entire screen, a thickness of a liquid crystal layer, that is, a cell gap has to be maintained highly precisely. In general, when the cell gap varies (decreases) by substantially 15% partially in a display area, the transmittance is deteriorated by substantially 4% to result in a visually observable level as the brightness unevenness.    Patent document 1: Japanese Patent Application Laid-Open No. 10-319408    Patent document 2: Japanese Patent Application National Publication No. 2004-524385    Patent document 3: Japanese Patent Application Laid-Open No. 06-148654    Patent document 4: Japanese Patent Application Laid-Open No. 2005-3750